High Dynamic Range (HDR) imaging is a digital imaging technique that captures a greater dynamic range between the lightest and darkest areas of an image. A process for automatically optimizing a dynamic range of pixel intensity obtained from a digital image is described in U.S. Pat. No. 7,978,258 to Christiansen et al. HDR takes several images at different exposure levels and uses an algorithm to stitch them together to create an image that has both dark and light spots, without compromising the quality of either one. However, HDR can present a distortion of reality because it distorts the intensity of the image overall. Accordingly, HDR techniques that enhance contrast without distorting the intensity of the image continue to be sought.
Techniques for enhancing an image of a biological sample are described in WO 2012/152769 to Allano et al. Among the problems with imaging such samples identified in Allano et al. are:                i) the size of the colonies being viewed;        ii) the proximity of one colony to another;        iii) the color mix of the colonies;        iv) the nature of the Petri Dish; and        v) the nature of the culture medium; as well as other factors.        
Allano et al.'s proposed solution to the problem of imaging a biological sample is to prepare a source image created from images obtained at each color, removing predetermined absorption effects for the culture medium and the culture vessel and determining a value for photon flux and exposure time using a predetermined exposure to obtain an image which is then dissected into luminosity zones. From that, image luminosity is obtained and used to determine if the value for photon flux and exposure time used was correct or if a new value for photon flux and exposure time should be used for image capture.
Problems with the above techniques is that they do not provide a system with an ability to provide imaging conditions that can detect very subtle changes in contrast that are required for image-based detection/identification of microbes on growth media. Because image-based evidence of microbes and/or their growth on media is (or at least can be) difficult to detect, more robust techniques for imaging such samples are sought.